FDA guidance: General Principles of Software Validation provides guidance on the validation of automated process equipment and quality system software,

In Europe, the regulation relies on the ISO 13485 standard, which has section 7.5 about validation of production processes, and their software.

Thus, these regulations and guidances are about production processes, only.

No regulatory requirement in development process

There's no regulatory requirement either in 21.CFR.820, or Medical Devices European Directive, for example, which tells you to validate software development tools.
There's no normative requirement either in IEC 62304, or more generally in ISO 13485.

Thus, validating tools used in a software development process is not mandatory.

The decision to validate development tools is only based on the conclusions of the risk assessment of the development process.

As I said in the article, these automated data processing systems shall be at first used in production processes, not development processes.

If you use Labview and NI Teststand to test printed circuit boards during production, to eliminate non-compliant batches, then this is an automated data processing system used in production and it is in the scope of ISO 13485 section 7.5 or 21 CFR 820.70. Thus you have to validate it to be compliant with regulations.

If you use Labview and NI Teststand to test a prototype at design time, then you are not in the case above. At design time, you are in section 7.3 of ISO or 21 CFR 820.30. And there is no such requirement to validate software tools used for design.

But:

If you product is very critical, for example a pacemaker, and if odds are not null that a failure of a tool used at design may result in a failure of the final product, then you will have to validate the tool.

For example, there is a chance that there are bugs in CUnit. If a unit test passes, instead of being failed, because of a possible bug in Cunit, then a bug could remain not detected by unit tests. In the case of software embedded in a pacemaker, such bug could result in a failure of the final medical device with severe consequences for the patient. Thus, given the severity of hazards generated by remaining bugs in CUnit, this tool should be validated.